Cosmetic preparations are essentially used for skincare. The skin is the largest human organ. Among its many functions (for example for heat regulation and as a sensory organ), the barrier function, which prevents the skin (and thus ultimately the entire organism) from drying out, is by far the most important. At the same time, the skin acts as a protective device against the invasion and the absorption of external substances (e.g. dirt, chemicals, microorganisms).
The main aim of cosmetic skincare is therefore to strengthen or restore this natural function of the skin as a barrier against environmental influences and against the loss of endogenous substances (as well as water, also natural fats, electrolytes etc.).
Another aim of skincare is to compensate for the loss by the skin of lipids and water caused by daily washing. This is particularly important if the natural regeneration ability is inadequate. Furthermore, skincare products should protect against environmental influences, in particular against sun and wind, and delay skin aging.
By far the most important type of product in the field of skincare compositions are emulsions. Emulsions are generally to be understood as meaning heterogeneous systems which consist of two liquids which are immiscible or miscible with one another only to a limited extent, which are usually referred to as phases. In an emulsion, one of the two liquids is dispersed in the other liquid in the form of very fine droplets.
Cosmetic or dermatological emulsions of the prior art consist of at least one fatty phase (fats and mineral oils, fatty acid esters, fatty alcohols etc.) and at least one water phase (water, glycerol, glycols etc.) which are dispersed in one another in the form of very fine droplets with the help of emulsifiers. If the oil phase is finely distributed in the water phase, then this is an oil-in-water emulsion (O/W emulsion, e.g. milk). The basic character of an O/W emulsion is defined by the water, i.e. it is less greasy on the skin, has more of a matting effect and absorbs more rapidly into the skin than a W/O emulsion.
The lipophilic phase of a bodycare emulsion usually comprises a mixture of oils, fats and waxes, the composition of which is to essentially influence the product-determining properties such as skincare and feel on the skin. Corresponding to the central importance of the oils, fats and waxes, a very broad range of these substances is commercially supplied and used.
For the purposes of this specification, oils, fats and waxes are referred to collectively as “oils” or “oil components”. Accordingly, the terms “oils” and “oil components” for the purposes of the present invention are to be understood as meaning the following compounds:                hydrocarbons        triglycerides        fatty esters or ester oils        
The group of hydrocarbons includes the various fractions of mineral oils and fats, and also squalene and squalane. A common feature of the compounds of this group is that they are constructed from straight-chain or branched-chain hydrocarbons. The hydrocarbons include, for example, paraffin oil, vaseline, hard paraffin, microcrystalline wax, mineral oils, ozokerite and ceresine.
Triglycerides are complete esters of glycerol with fatty acids. The compounds of this group usually form an essential constituent of lipid-containing cosmetic preparations. This group includes the naturally occurring (vegetable and animal) oils (for example avocado oil, olive oil, corn oil, mink oil, castor oil, soybean oil, sunflower oil and sesame oil, to name but a few) and fats (e.g. Japan wax, cocoa butter and the like). Synthetic triglycerides which are prepared by esterification of fatty acids with glycerol also belong to this group.
Through the esterification of fatty alcohols with organic mono-, di- and polycarboxylic acids or short-chain alcohols with long-chain fatty acids, it is possible to prepare a large number of fatty esters which are customarily used very widely in cosmetic preparations. This group includes, inter alia, monocarboxylic esters (for example butyl stearate, cetyl palmitate, decyl oleate, 2-ethylhexyl palmitate, hexyl laurate, isopropyl isostearate, lanolate, laurate, linoleate, palmitate, stearate, to name but a few), dicarboxylic esters (e.g. diisopropyl adipate, cetyl, lauryl and myristyl lactate and diglycerol esters of caprylic, capric and succinic acid and the like), and alkyl benzoates.
The use of oil components in cosmetic or dermatological preparations is acceptable per se. Nevertheless, oils, like ultimately every chemical substance, can in individual cases cause allergic reactions or reactions based on hypersensitivity of the user. Thus, for example, various oils are also suspected, with exposure to sunlight, of triggering photodermatoses, which are also referred to as “Mallorca acne”.
Moreover, oil-containing cosmetic and dermatological preparations have the disadvantage that they have comedogenic activity, i.e. they can cause or aid the formation of skin symptoms which are characterized by noninflammatory and inflammatory papules. Starting from blocked hair follicles (comedones), such skin symptoms can lead to pustule, abscess and scar formation. The most common is Acne vulgaris, which occurs primarily in puberty. Causative conditions are the keratinization and blocking of the hair follicle opening.
Moreover, oil-containing cosmetic and dermatological preparations can produce a greasy and sometimes sticky impression on the skin and are difficult to distribute, particularly on skin covered with hair. In individual cases, they may therefore not even be marketable since they are unacceptable to or are viewed negatively by the consumer.
However, in cosmetic or dermatological light protection preparations of the prior art in particular, at least when high sun protection factors (e.g. greater than SPF 15) are to be achieved, oils have hitherto been necessary to dissolve lipophilic filter substances.
Although, when viewed from a thermodynamic viewpoint, emulsions are unstable systems, it is possible to prepare emulsions which are stable for years. An emulsion is described as stable if, over a predefined period of time, no measurable temporal or spatial changes in the droplet size distribution can be established.
The stability or instability of emulsions depends on a variety of factors. Firstly, the water phase of a W/O emulsion tends, for example, toward sedimentation since the water and oil phases have different densities. The oil phase of an O/W emulsion, accordingly, has a tendency toward creaming.
In addition, because of the forces of attraction between the finely distributed droplets of the disperse phase, drop aggregation can result, where the individual droplets of an aggregate remain initially separate from one another by a thin film of the continuous phase. In this case, the original droplet size distribution only appears to change and can in this case be restored by stirring or shaking.
However, the droplets which are in contact can, moreover, also coalesce, which leads to a real change in the droplet size distribution, which can only be changed back by inputting energy. This phenomenon is referred to as coalescence. The more viscous the outer phase of the emulsion, the more slowly the process of coalescence proceeds.
The processes described can occur individually or together. One process often initiates or intensifies the other. Thus, for example, the formation of aggregates in O/W emulsions accelerates creaming of the oil phase. If the disperse state of an emulsion is partially or even completely lost, then the two phases separate, and this is referred to as emulsion breaking.
Accordingly, the stabilization of emulsions over a relatively long period of time requires auxiliaries which prevent separation of the two phases, or at least delay it until the emulsion has fulfilled its intended purpose.
These auxiliaries should firstly stabilize the interface by preventing the droplets of the disperse phase from coalescing. In the ideal case, these substances moreover effect repulsion of the droplets, which prevents them from contacting, thus avoiding agglomeration (aggregate formation).
Secondly, auxiliaries are used to counteract creaming or sedimentation of the phases.
Emulsifiers are interface-active substances which are able to prevent the interfacial tension between external and internal phase by positioning themselves preferably at the interface between these two phases. This is made possible as a result of their amphiphilic molecular structure: emulsifiers have at least one polar (hydrophilic) group and at least one nonpolar (lipophilic) group. As a result, they are soluble both in the hydrophilic phase and in the lipophilic phase. The part which is more soluble in the corresponding phase protrudes into this phase and as a result lowers the interfacial tension between the two phases.
The attempt to classify emulsifiers is difficult since they belong to categories which are very different in chemical terms. The more quickly an emulsifier lowers the interfacial tension and the lower the equilibrium value of the interfacial tension, the more effective the emulsifier.
Moreover, emulsifiers also stabilize emulsions as a result of the formation of interfacial films and thus “physical” barriers, as a result of which aggregate formation and coalescence of the emulsified particles is prevented. As a result of the positioning of the emulsifier at the interface, the droplets either become charged, so that they mutually repel, or a stable, often high-viscosity or even solid protective layer is formed around the droplets.
However, for the practical preparation of cosmetic or dermatological emulsions, the use of one or more emulsifiers on their own is generally insufficient. Important factors for the stability of cosmetic or dermatological preparations are also:                very fine distribution of the two phases in one another:        the smaller the dispersed particles, the more stable the emulsion.        high viscosity of the outer phase        a stable interfacial film        a balanced phase volume ratio        
The emulsifier system must therefore in most cases comprise, in addition to the actual emulsifier, a further component which is referred to as coemulsifier, stabilizer or, depending on the activity mechanism, also as bodying agent, thickener or protective colloid etc.
These substances, which for the sake of simplicity are referred to below as stabilizers, increase the stability of an emulsion. Stabilizers must not be interface-active, but can be amphiphilically constructed compounds.
One way of stabilizing emulsions is, in accordance with that stated above, to increase the viscosity of the outer phase. This viscosity increase generally brings about a considerable reduction in the mobility of the dispersed droplets, as a result of which the rate of sedimentation or creaming is reduced. As a result of this, the droplets also meet less frequently, which results in a lower tendency toward coalescence.
The viscosity of the external phase can, for example, be increased by adding thickeners which form, for example, gels and/or lamellar liquid crystals. In principle, emulsifiers are also able to increase the viscosity of a liquid as a result of the formation of emulsifier gel networks. However, this requires a relatively large amount of emulsifier since gel networks are only formed when the total interface between the phases is coated with emulsifier molecules.
The breaking of an emulsion can also be prevented by the choice of a suitable phase volume ratio. To illustrate this fact, imagine an emulsion as a system of metal spheres of equal diameter (internal phase) and a liquid (external phase). Sedimentation or creaming can, in this simple model, no longer occur if the entire liquid is filled with metal spheres. Assuming as dense as possible a sphere packing as distribution, this is the case precisely at a ratio of 1:2, i.e. when ⅔ of the emulsion consists of an internal phase. It is obvious that the viscosity of an emulsion increases as the proportion of internal phase grows since the mobility of the dispersed droplets becomes restricted as a result.
The person skilled in the art is of course aware of the large number of options for formulating stable emulsions, i.e. multiphase systems of oil components and water in addition to further auxiliaries and additives for cosmetic or dermatological use, for example in the form of creams and ointments, which are spreadable in the range from room to skin temperature, or as lotions and milks, which are flowable in this temperature range. In this connection, as well as the choice of the “correct” emulsifier or emulsifier system, the further composition of the preparation, in particular, is important.
Emulsions of “liquid” (=flowable) consistency are used in cosmetics, for example as care, cleansing, face or hand lotions. They generally have a viscosity of from about 2 000 mPa·s to about 10 000 mPa·s. The stability of flowable emulsions requires particular attention since the considerably greater mobility of the particles encourages more rapid coalescence.
Disadvantages can, for example, lie in the fact that relatively large amounts of one or more emulsifiers are required (e.g. 3% by weight or more). Since, however, even emulsifiers, like ultimately every chemical substance, can in individual cases trigger allergic reactions or reactions based on hypersensitivity of the user (although the use of customary cosmetic emulsifiers is of course generally entirely acceptable), it is desirable to keep the emulsifier content of a cosmetic or dermatological formulation as low as possible.
Emulsions with a very low viscosity (low-viscosity or sprayable emulsions) have hitherto, in accordance with that stated above, only been able to be formulated with considerable effort, if at all. Accordingly, the supply of such formulations is extremely low. Nevertheless, such formulations could offer the consumer cosmetic results which are hitherto unknown.